中国前寒武纪地层年代学研究的进展和相关问题

Advances in the study of Precambrian chronostratigraphy in China:A review

总结了中国近十年在前寒武纪年代地层研究方面的主要进展，包括：（1）近年获得的大量锆石SHRIMP和LA-ICPMSUPb年龄，华北克拉通早前寒武纪BIF和相关地层主要形成于新太古代；（2）新的同位素年龄表明，一些以往认为是早前寒武纪的地层或地质体（康定岩群、额尔古纳岩群）的主体是新元古代的地质体；（3）大量的锆石原位定年数据表明，华北克拉通北缘的孔兹岩系主要形成于古元古代晚期；（4）长城群的底界年龄应小于1670Ma，很可能在1650Ma左右；（5）根据新的同位素年龄对中元古代的年代地层格架进行了重新划分；（6）大量新的同位素年龄数据揭示华南地区以往认为是中元古代的地层（板溪群等）实际应是新元古代的。随着研究深入也提出了需要研究的新问题，这些问题包括：（1）2．5～2．3Ga是否存在缺少地质记录的寂静期？（2）长城系下部的地层何在？（3）中元古代上部系级年代地层单位的建立；（4）青白口系岩石地层单位的完善。

The major advances in the study of Precambrian chronostratigraphy since the 3rd Stratigraphic Congress of China held in 2000 are described in this paper. The major advances in six aspects are listed below： （1） Abundant zircon SHRIMP and LA-ICPMS UPb data obtained in resent years indicate that BIFs and related strata in the North China Craton mainly formed during the late Archean （2.55- 2.50 Ga）. （2） Some geological bodies and strata （Kangding complex, Sichuan; Erguna group, in Xing＇ an area） traditionally regarded as of the early Precambrian have demonstrated that these compIex and strata were mainly formed during the Neoproterozoic time. （3） A lot of zircon U-Pb ages confirmed that khondalite series in the north margin of the North China Craton mainly formed in the late Paleoproterozoic. （4） The base age of the Changcheng group should be younger than 1670 Ma, probably close to 1650 Ma. （5） The geochronological framework of the Mesoproterozoic strata has been revised by new isotopic ages. （6） Abundant new zircon ages demonstrate that the strata （Banxi group etc. ） in South China block traditionally regarded as the Mesoproterozoic were formed during the Neoproterozoic time. As the research progressed, a number of new problems arose. These problems include that （1） whether there was an age gap between 2. 45- 2. 30 Ga.？ and that （2） where is the bottom strata of the Cbangcheng system.？ and that （3） the further perfection of the Qingbaikou system.